Java 子类构造函数

这是主要课程

    **
** Assignment class
**
** This class represents an Assignment. 
**
****************************************************/
public class Assignment {
private String name;
private double pointsPossible;
private double pointsEarned;

 // Assignment constructor
 //
// postcondition: all instance variables are initialized with
// the given values. 
public Assignment (String n, double ptsPoss, double ptsEarned) {
 name =n;
pointsPossible=ptsPoss;
pointsEarned=ptsEarned;
 }
// getName accessor method
 //
 // postcondition: returns the name of this Assignment public 
String getName() {
return name;
    }

// getPointsPossible accessor method
//
// postcondition: returns the points possible for this Assignment
public double getPointsPossible() {
return pointsPossible;
    }
 // getPointsEarned accessor method
//
// postcondition: returns the points earned for this Assignment
public double getPointsEarned() {
return pointsEarned;
 }
}

当我试图在我的子类中使用我的访问器时，我在初始化它的变量时遇到了一个错误

下面是子类

import java.util.ArrayList;
/****************************************************
**
** CategoryAssignment class
**
** This class represents an CategoryAssignment. 
** Do not add any additional methods to this class.
**
****************************************************/
public class CategoryAssignment extends Assignment {
    // declare any new instance variables that you need here
    // don't forget to make them private!
    // don't declare more that you really need!
    // CategoryAssignment constructor
    //
    // postcondition: all instance variables are initialized with
    // the given values.     
    public CategoryAssignment (String n, double ptsPoss, double ptsEarned, String cat) {

    }

    // getCategoryName accessor method
    //
    // postcondition: returns the name of the category associated
    // with this CategoryAssignment
    public String getCategoryName() {
        return cat;
    }
}

---

我无法初始化子类的变量。此外，作为一个成绩册项目，将categories变量存储在数组或ArrayList中是否明智？

Java中没有隐式构造函数链接，即使子类和超类构造函数具有相同的签名。您需要使用

super

关键字显式地将参数传递给超类的构造函数：

public CategoryAssignment
    (String n, double ptsPoss, double ptsEarned, String cat) {
    super(n, ptsPoss, ptsEarned, car);
}

---

我认为您需要考虑从子类调用基类上的构造函数

public CategoryAssignment (String n, double ptsPoss, double ptsEarned, String cat) {
    base(n, ptsPoss,ptsEarned, cat);
}

---

您的子类

categoryaSignment

不应该调用超级类构造函数吗？比如：

public CategoryAssignment (String n, double ptsPoss, double ptsEarned, String cat) {
    super(n, ptsPoss, ptsEarned);
    this.cat = cat;
}

您还需要在

类别签名

中定义

字符串cat

属性

关于你的第二个问题“这也是一个成绩册项目，将categories变量存储在数组或ArrayList中是否明智？”，据我在getter中看到的，

cat

变量是一个字符串。很难说列表或数组是否最适合您提供的信息。

首先： 如果你想访问这个函数，你必须在你的类中声明变量cat。您必须在类中添加以下内容：

    private String cat;

下一步： 子类构造函数中的第一条语句是超类的构造函数。就你而言：

    public CategoryAssignment(String n, double ptsPoss, double ptsEarned, String cat) { 
       super(n, ptsPoss, ptsEarned);
       this.cat = cat; 
    }

---

什么错误？请出示stacktrace。另外，请正确设置代码的格式。我从未看到类中定义的

cat

。此外，未定义成员

cat

（第二个类中的注释部分详细说明了这一点）。此问题是用JAVA编写的，而不是用C编写的#